Corrosion inhibitor in absorption refrigeration system



Jan. 1, 1952 wm 2,580,984

CORROSION INHIBITOR IN' ABSORPTION REFRIGERATION SYSTEM Original Filed Feb. 8, 1946 g IWNVENTOR.

Patented Jan. I, 1952 CORROSION INHIBITOR IN ABSORPTION REFRIGERATION SYSTEM Nils Erik Widell, Stockholm, Sweden, assignor to Aktiebolaget Elektrolux, Stockholm, Sweden, a corporation of Sweden Original application February 8, 1946, Serial No. 646,394. Divided and this application May 12, 1951, Serial No. 225,934. In Sweden January 2 Claims.

This invention relates to absorption refrigerating apparatus and more particularly to such apparatus of the inert gas type wherein the ab- Sorption solution contains a corrosion protective substance. This application is a division of my application Serial No. 646,394, filed February 8, 1946.

The main object of the invention is to increase the lifetime of the apparatus and to prolong the durability of the corrosion protection. The invention is of particular importance in such refrigerating apparatus wherein absorption solution from its normal circulating system through the boiler and absorber of the apparatus is brought into contact with working medium having a higher refrigerant concentration than that of the absorption solution.

The invention will be hereinafter more fully described with reference to the accompanying drawing showing diagrammatically an embodiment of the arrangement according to same and in this connection further characteristic features of the invention will be set forth.

The figure shows diagrammatically an absorption refrigerating apparatus. wherein water is used as an absorbent and ammonia as refrigerant. Referring to the figure reference numeral ill denotes a tube acting as aflue, to which heat is continuously supplied from a heat source, not shown, for example an electric cartridge, a gas or petroleum burner. The boiler of the apparatus is designated by H and its liquid circulating pump by H. The boiler pipe ii is' extended upwardly and at the top connected to the air cooled condenser ii of the apparatus. Further numeral M denotes a so-called pressure equalizing vessel of a kind known per se which through a drainage conduit I 5 communicates with the evaporator of the apparatus designated by l8. In said conduit [5 the condenser pipe It opens, from which liquid refrigerant thus flows by gravity to the evaporator through the conduit l5. Further numeral ll designates the gas heat exchanger of the apparatus and [8 its air-cooled absorber. Numeral 49 indicates a vent conduit through which the pressure equalizing vessel It freely communicates with the gas circulating system of the apparatus. Said system is formed in a way known per se as is the liquid circulating system of the apparatus. The enriched solution in the absorber vessel 20 of the apparatus thus streams through its liquid heat exchanger 2| and the main pump II to the boiler H and thence it returns through the heat exchanger fl and a conduit 22 to the absorber It.

In accordance with usual practice the appa- 2 ratus is formed of iron pipes Joined together by gas welding. Before filling the apparatus it is evacuated of all air, and as ammonia by itself has no influence upon iron in absence of oxygen, no corrosion should be feared in the internal iron walls. However, these walls formed of ferrous metal will nevertheless be affected by the ammonia solution by the forming of complicated iron compounds, by which the walls after a relatively short time would be loosened up and lose their strength against the high pressure (about 20 atm.) prevailing in the apparatus. In order to avoid such corrosion an alkali salt of sodiuni chromate (Na2CrO4) has previously been dissolved in the absorption solution. The chromatic concentration required in the absorption solution for counteracting the corrosion is extremely small and may be counted in fractions of per cent. However, the chromate is slowly consumed and therefore it has previously been necessary to utilize a concentration of chromate in the solution many times higher for the purpose of creating a chromatic reserve, covering several years consumption. Salts dissolved in the absorption solution will, however, influence the pumping in the thermosiphon pump I! in an unfavourable direction and therefore until now it has been necessary to limit the concentration of chromate in the solution to a concentration corresponding to about 2% of CrOa.

In different ways, however. it has been attempted to form an additional reserve of alkali chromate by enclosing in' the absorber vessel a storage of solid sodium chromate in a container with a limited communication with the surrounding solution, whereby a gradual dissolving of the solid chromate has been attained. It has not been possible to make the dissolving so uniform that the concentration of the solution with security can be kept below the values wanted. The velocity of dissolving has also appeared to be dependent upon a plurality of uncontrollable fac-' tors, among other things the operating temperature which very essentially varies with the oilmatic condition under which the apparatus is operated. According to this invention a reserve of chromate of an arbitrary greatness may be arranged in the apparatus. The invention is substantially characterized thereby that the absorption solution of the apparatus is saturated with a salt of the chromatic acid, having a solubility in said solution not exceeding 2%. Further, the solubility of the present chromate may be as much as possible independent of the temperature", though certain variations with the temperature may be permitted. A particularly suitable chrodissolved in the absorption solution will be comconsumed. Itis'therefore genparatively rapidly erally necessary to enclose a reserve of solid strontium chromate in the apparatus. Accordir. g to the invention therefore a container 50 is arranged in the absorber vessel 20 or possibly in another vessel interconnected with the liquid circulating system of the apparatus. The reservoir Sll may suitably include a short piece of pipe, both openings of which are coveredwith a fine-meshed iron net and in which a pressed tablet of strontium chromate is inserted. The container may suitably be attached to the wall of the vessel by a strip .or similar member which is attached to the .wall of the vessel and to the wall of the container 0 by welding. The support is denoted by Ill when the liquid contents of the absorber vessel is continuously renewed, the absorption solution will automatically become saturated gradually as its contents of chromate decreases during its passage through the absorber vessel 20. The pressing of the solid strontium chromate into a tablet possesses the advantage that no solid particles by mechanical influence of the streaming solution will follow the liquid through the narrow passages of the apparatus. In order to improve the strength of the tablet small amounts of sodium hydroxide may be mixed with the chromate when pressing said tablet.

As already mentioned, the invention is of particular importance in such absorption refrigerating apparatus in which the absorption solution is now and then brought into contact with liquid refrigerant, the concentration of which thus attains high values. This is the case in the absorption refrigerating apparatus shown in the figure. From the lower part of the boiler pipe a conduit 23 runs out, which opens into the pressure equalizing vessel i4 and forms an auxiliary pump for raising the absorption solution to said vessel. Thence, the warm solution streams through the conduit i5 into the evaporator coil 18 and thence through the exchanger l1 and the absorber I! to the absorber vessel 20. In contradistinction to the main pump 12 the auxiliary pump 23 is not immediately heat conductively connected with the fine it but instead arranged in heat conducti-ve relation with a hermetically closed heat transfer system which is welded to the flue l0 along a welded seam 42. The system contains a heat transfer medium with a high boiling point, possibly in addition to an auxiliary medium with a lower boiling point. The transfer medium is vaporized in the boiling part ll of the system and condenses to liquid in a container where the condensate is accumulated. Some part of the vapours, however, give off their heat contents to the pump pipe 23. After a certain period the system is boiled dry, and all the condensate remains stor- I aged in the container 30.

thus permitting it to be raised for tilting the liquid contents. In this way a method of controlling the heat transfer system is attained, thus causing the pump 21 to operate whenever desired and after a certain period automatically to stop working. The solution raised by the auxiliary pump 23 streams in the'way already described into the evaporator where it, however, is mixed with refrigerant condensate entering from the condenser 13, having an ammonia concentration from to The supply of condensate from the condenser It takes place continuously. This supply of absorption solution to the evaporator I! has for its object, when required, to effect melting of ice formed thereon. It has appeared that a solution of sodium chromate of 1 to 2 per cent cannot be mixed'with ammonia having the concentration existing in the evaporator without most of the salt being precipitated into solid form. The salt precipitated would collect in the evaporator and would very soon effect a blocking action and at the same time such precipitated salt for the future would be prevented from taking part of the corrosion protection. A solution of strontium chromate remains, even if it is saturated, approximately un effected by an increase of the ammonia concentration and the small amounts of chromate which possibly may be precipitated willbe replaced from the reverse 50 provided in the absorber vessel.

Though the strontium chromate is very littie soluble in the absorption solution, that is, in the ammonia water mixture, the concentration of protecting substance in this chemical compound is suflicient to effect a satisfying corrosion protection.

What is claimed is:

1. In the art of refrigeration employing an absorption refrigeration system formed of ferrous metal and utilizing ammonia as refrigerant and water as an absorbent, that improvement which comprises maintainingin the aqueous ammonia solution a supply of solid strontium chromate.

2. In the art of refrigeration employing an absorption refrigeration system formed of ferrous metal and utilizing ammonia as refrigerant and water as an absorbent, that improvement which comprises maintaining in the aqueous ammonia solution a solid body of matter including strontium chromate and sodium hydroxide mixed therewith.

REFERENCES CITED Widell Dec. 28, 1946 Tl'iia container is oonnected by a flexible member 8| with the system, 

1. IN THE ART OF REFRIGERATION EMPLOYING AN ABSORPTION REFRIGERATION SYSTEM FORMED OF FERROUS METAL AND UTILIZING AMMONIA AS REFRIGERANT AND WATER AS AN ABSORBENT, THAT IMPROVEMENT WHICH COMPRISES MAINTAINING IN THE AQUEOUS AMMONIA SOLUTION A SUPPLY OF SOLID STRONTIUM CHROMATE. 